Migration guide from Apollo ROS¶

This article describes the essential changes for projects to migrate from Apollo ROS (Apollo 3.0 and before) to Apollo Cyber RT (Apollo 3.5 and after). We will be using the very first ROS project talker/listener as example to demonstrate step by step migration instruction.

Build system¶

ROS use CMake as its build system but Cyber RT use bazel. In a ROS project, CmakeLists.txt and package.xml are required for defining build configs like build target, dependency, message files and so on. As for a Cyber RT component, a single bazel BUILD file covers. Some key build config mappings are listed below.

Cmake

project(pb_msgs_example)
add_proto_files(
  DIRECTORY proto
  FILES chatter.proto
)
## Declare a C++ executable
add_executable(pb_talker src/talker.cpp)
target_link_libraries(pb_talker ${catkin_LIBRARIES}pb_msgs_example_proto)
add_executable(pb_listener src/listener.cpp)
target_link_libraries(pb_listener ${catkin_LIBRARIES}  pb_msgs_example_proto)

Bazel

cc_binary(
  name = "talker",
  srcs = ["talker.cc"],
  deps = [
    "//cyber",
    "//cyber/examples/proto:examples_cc_proto",
    ],
  )
cc_binary(
  name = "listener",
  srcs = ["listener.cc"],
  deps = [
    "//cyber",
    "//cyber/examples/proto:examples_cc_proto",
    ],
  )

We can find the mapping easily from the 2 file snippets. For example, pb_talker and src/talker.cpp in cmake add_executable setting map to name = "talker" and srcs = ["talker.cc"] in BUILD file cc_binary.

Proto¶

Apollo ROS has customized to support proto message formate that a separate section add_proto_files and projectName_proto(pb_msgs_example_proto) in target_link_libraries are required to send message in proto formate. For config proto message in Cyber RT, it’s as simple as adding the target proto file path concantenated with name of cc_proto_library in deps setting. The cc_proto_library is set up in BUILD file under proto folder.

cc_proto_library(
  name = "examples_cc_proto",
  deps = [
    ":examples_proto",
  ],
)
proto_library(
  name = "examples_proto",
  srcs = [
    "examples.proto",
  ],
)

The package definition has also changed in Cyber RT. In Apollo ROS a fixed package package pb_msgs; is used for proto files, but in Cyber RT, the proto file path package apollo.cyber.examples.proto; is used instead.

Folder structure¶

As shown below, Cyber RT remove the src folder and pull all source code in the same folder as BUILD file. BUILD file plays the same role as CMakeLists.txt plus package.xml. Both Cyber RT and Apollo ROS talker/listener example have a proto folder for message proto files but Cyber RT requires a separate BUILD file for proto folder to set up the proto library.

Apollo ROS¶

CMakeLists.txt
package.xml
proto
- chatter.proto
src
- listener.cpp
- talker.cpp

Cyber RT¶

BUILD
listener.cc
talker.cc
proto
- BUILD
- examples.proto (with chatter message)

Update source code¶

Listener¶

Cyber RT

#include "cyber/cyber.h"
#include "cyber/examples/proto/examples.pb.h"

void MessageCallback(
    const std::shared_ptr<apollo::cyber::examples::proto::Chatter>& msg) {
  AINFO << "Received message seq-> " << msg->seq();
  AINFO << "msgcontent->" << msg->content();
}

int main(int argc, char* argv[]) {
  // init cyber framework
  apollo::cyber::Init(argv[0]);
  // create listener node
  auto listener_node = apollo::cyber::CreateNode("listener");
  // create listener
  auto listener =
      listener_node->CreateReader<apollo::cyber::examples::proto::Chatter>(
          "channel/chatter", MessageCallback);
  apollo::cyber::WaitForShutdown();
  return 0;
}

ROS

#include "ros/ros.h"
#include "chatter.pb.h"

void MessageCallback(const boost::shared_ptr<pb_msgs::Chatter>& msg) {
  ROS_INFO_STREAM("Time: " << msg->stamp().sec() << "." << msg->stamp().nsec());
  ROS_INFO("I heard pb Chatter message: [%s]", msg->content().c_str());
}

int main(int argc, char** argv) {
  ros::init(argc, argv, "listener");
  ros::NodeHandle n;
  ros::Subscriber pb_sub = n.subscribe("chatter", 1000, MessageCallback);
  ros::spin();
  return 0;
}

You can see easily from the two listener code above that Cyber RT provides very similar API to for developers to migrate from ROS.

ros::init(argc, argv, "listener"); –> apollo::cyber::Init(argv[0]);
ros::NodeHandle n; –> auto listener_node = apollo::cyber::CreateNode("listener");
ros::Subscriber pb_sub = n.subscribe("chatter", 1000, MessageCallback); –> auto listener = listener_node->CreateReader("channel/chatter", MessageCallback);
ros::spin(); –> apollo::cyber::WaitForShutdown();

Note: for Cyber RT, a listener node has to use node->CreateReader<messageType>(channelName, callback) to read data from channel.

Talker¶